The present invention relates generally to machining apparatus, and more particularly to a system for compensating for slight variations in the straightness and roll of the tool path used on the machine. This invention was made in the course of, or under a contract with the United States Department of Energy.
Specification requirements for machined components used in many technological fields have become increasingly stringent and are often within tolerances of less than 100 microinches. Such machining frequently involves the use of a high precision, low vibration machine tool with diamond tooling. For example, diamond machined metal mirrors for reflecting laser beams in nuclear fusion systems require a reflective surface with a flatness deviation of less than 20 microinches. In order to maintain a 20-microinch mirror the slideway path straightness and/or roll error must be less than approximately 10 microinches. Most state of the art precision machines capable of such machining exhibit slideway straightness deviation of about 25-35 microinches and a flatness (vertical variation over the length of the slide causing roll of the workpiece or tool fixture) of about 10 to 20 microinches.
Several techniques for minimizing the effects of slideway straightness and/or roll have been used but have met with only limited success. For example, a previous approach was to use the slide positioning motor and lead screw disposed along one of the axes to make necessary corrections during machine operation. However, the friction in the slides and the small incremental movements required to correct for non-straightness and/or roll have caused this approach to have only limited success. Alternatively, reworking the slides to correct for errors in roll and straightness was found to be very time consuming and expensive, as well as requiring specialized personnel. Normally such reworking does provide slide straightness better than about 20 microinches but it was found that the slide straightness changed sufficiently with use as to necessitate frequent reworking.